The present invention relates to a method and apparatus for processing oily wastewaters, such as bilge water from ships, boats and the like.
Numerous processes and activities produce wastewater which is contaminated with oil. For example, the bilge water which leaks into ships or boats frequently becomes contaminated with oil leaked or spilled from machinery or tanks on the vessels. Many industrial processes, such as machining of metal, also produce wastewater contaminated with oil.
Current environmental laws encourage both waste minimization and resource recovery while current economic conditions require them. The rapid consumption of inherently limited petroleum deposits by modern industrial societies makes it economically desirable to recover and reuse oil. Ecological considerations also have led governments to promulgate environmental regulations which prohibit disposing of oily wastes in such a way as to contaminate the environment. Yet currently available technologies for recovery or disposal tend to be expensive or less than fully effective. Thus, while both economic and environmental considerations make it desirable to recover oil from wastewater, considerable difficulty may be encountered in attempting to separate and recover oil from oily wastewaters.
Oily wastewaters generally contain oil in two forms. The first is free oil which is simply intermixed with the aqueous phase. The second form is emulsified oil in which tiny particles of oil are stably dispersed throughout the aqueous phase. Although oil and water are generally immiscible, it is often costly and time consuming to separate them, and in some cases it is so difficult as to be considered impractical. The difficulties are compounded when the proportion of oil in a wastewater is small, e.g., less than about 10 percent. Despite the great deal of effort which has been expended in this field, there remains a need for improved methods and apparatus for treating oily wastewater to separate the oil from the water.